Mikania micrantha extract/KI blend as a novel synergistic inhibitor for steel corrosion in concentrated H3PO4 solution

Abstract

Mikania micrantha extract (MME) was prepared by reflux extraction from the exotic invasive weed of Mikania micrantha using ethanol water solution as the solvent. The synergistic inhibition effect and mechanism of MME and potassium iodide (KI) on the corrosion of cold rolled steel (CRS) in 4.0 M H3PO4 solution was investigated by gravimetric, electrochemical and surface analysis techniques for the first time. The results show that either MME or KI has moderate inhibitive action, and the maximum inhibition efficiency is below 65 % at 20 ℃. However, incorporation MME with KI can produce a synergism (s > 1), and obtain a pleasant inhibition of 92.9%. The adsorption of MME on CRS surface obeys Freundlich isotherm, while KI and MME/KI complex follow Langmuir isotherm. They are all mixed-type inhibitors, and MME/KI mixture significantly retards the electrochemical corrosion comparing with individual MME or KI. The process of electrochemical corrosion is controlled by charge transfer, and the charge transfer resistance follows the order of MME/KI > KI > MME. SEM and AFM demonstrate that the corrosion of CRS surface is efficiently retarded by the blend of MME and KI. From FTIR and XPS analysis, the formed layer of the synergistic inhibited CRS surface is mainly composed of the organic compounds with polar groups in MME. There is also a synergistic inhibition of the major components (rutin, quercetin, chlorogenic acid and ferulic acid) with KI. MME/KI can be deemed as a novel efficient inhibitor for steel in concentrated phosphoric acid, which develops an original path for the utilization of Mikania micrantha in the field of metallic corrosion and protection.